It is common practice to test the corrosive effects of certain materials on the storage or transport apparatus in which such materials are confined by inserting a sample coupon or electrical element made from the same material as the storing or transporting apparatus within these apparatus and the material contained therein for a predetermined time. A coupon must also be removed for further analysis whereas an electrical element is replaced after its predetermined life. In unpressurized environments, such as an open tank, and low pressure environments, the coupons and electrical elements may be inserted within the container without the use of any special tools. However, when testing materials in a pressurized environment, such as a pipeline, pressure vessel, condenser and heat exchanger, the sample coupon or electrical element must be inserted and retracted from the environment without permitting communication of the pressurized environment with the atmosphere.
Packing glands currently exist through which an elongated probe is inserted in hermetically sealed engagement therein. The packing glands are detachably connected to a valve which is connected to and communicates with the pressurized environment. To insert a sample coupon or electrical element into the pressurized environment, the gland is detached from the valve and the coupon or electrical element is attached to the end of the rod extending within the gland. The gland has a chamber in which the coupon or electrical element is contained during attachment of the gland to the valve. Once the electrical element or coupon is connected to the rod and the gland is attached to the valve, the valve is opened thereby pressurizing the chamber. The rod is inserted axially within the gland thereby positioning the coupon or electrical element within the pressurized environment.
To remove the coupon or electrical element, the coupon or electrical element is retracted within the chamber by retracting the probe through the gland. The valve is closed, pressure is bled from the chamber and the gland is detached from the valve to access the coupon or the element. The probe can be manually inserted into low pressure environments, however, at higher pressures the probe cannot be inserted or safely retracted without mechanical aid.
Probe retraction tools exist for inserting probes into high pressure environments. Examples of such retractor tools are the "Standard Retractor Tool" and the "Special Retractor Tool" manufactured by Accurate Corrosion Monitoring Company. The "Special Retractor Tool" has a base, a vertically extending vertical worm gear, a plate connected to the worm gear and vertically moved thereon by the rotation of the worm gear and a means for rotating the worm gear. The base is detachably connected to a packing gland and the probe is secured to the plate in parallel relation to the worm gear. To insert the rod, the worm gear is rotated, thereby urging the shaft into the packing gland. Note that since the worm gear and the probe are not coaxial in relation, a torqueing force is exerted on the worm gear through the plate by the pressurized environment's influence on the probe. At extremely high pressures such torqueing forces could damage the retractor tool, specifically the worm gear, and at best bind the plate with the worm gear thereby hindering the vertical movement of the plate.
The "Standard Retractor Tool" has a cylindrical casing that threadably engages certain packing glands adapted for such threaded connection, an elongated screw threadably connected to the top of the casing and extending therein, a handle connected to the top of the screw for rotating the same and a means for connecting the screw to the upper end of the probe.
The use of a solid worm gear or screw to insert the probe presents a functional dilemma in that either the screw is too thin to accommodate use with extremely high pressures or, if manufactured thick enough for such pressures, the weight of the worm gear or screw makes the retraction tool cumbersome and difficult to efficiently operate.
A retractor using an oversized threaded screw shaft is best exemplified in the COSASCO Retractor which includes a base for engaging an insertion gland, the oversized screw connected to the base and extending vertically therefrom, means for engaging the probe and means for urging the probe parallel the length of the oversized screw.
A probe retractor manufactured by Rohrback Instruments, a division of Rohrback Corporation, has a pair of parallel rotatable shafts mounted in an aluminum frame with means for engaging a probe threadably mounted to both shafts. To urge the means for engaging along a vertical path, both shafts must be rotated simultaneously. The apparatus is designed for use by two operators.